Low voltage heating circuit



March 25, 1958 D. MORRISON 2,323,405

LOW VOLTAGE HEATING CIRCUIT Filed Jan. 13. 1954 a; 172M??? far 5y Jar/rr & Cartier v Jim/7205.5

United States Patent lndiistries,.lnc. Sycamore; 111;,2aacorporation ofvDeiaware:

kp'plicationlanuary 1a; 1954', Serial .No. 403,687

l'Claim. Cl. 219-40 My invention resides in the field of apparatus forheating metal pieces. to. a predetermined temperature range so that theycan besoldered, fused, or otherwise suitably, secured together by theapplication of'heat.

More specifically, my invention relates to an electricaldevice forheating aluminum tubing, or the like; so that it can be maintainedbetween two predeterminedtemperatures within a selected temperaturerangefor a predetermined period of time so that the aluminum tubing willsoak or heat' for a selected period in the desired temperature range.

A primary object of my invention is an electrical heating devicegenerally of the above-described character for bringing. aluminumtubing: upto a: predeterminedtemperature range, and maintaining itwithin that temperature. range for a predeterminedperiod of time.

Anothcr.object isanelectrical heating device of 'the above-describedcharacter which requires very littletsupervision, by the. operator oncethe aluminum tubing has been clamped in position and the device turnedon by the operator.

Another object is an electrical heating device of the above-describedcharacter which will very accurately maintain aluminum tubing 01'similar pieces between an upper and lower temperature which describesthe temperature range, and will oscillate the temperature of thealuminum tubing back and forth between these two limits for apredetermined period of time.

Other objects will appear from time to time in the ensuing specificationand drawing in which a schematic wiring diagram with various associatedparts of my invention is diagrammatically illustrated.

In the drawing, a conventional source of line current is provided at 10,it being understood that this current is the usual 115 volts A. C. Thecurrent is carried to the invention through a pair of conventional leads12 and 14. A manually operable switch 16 is provided in the line 14, butit could be in either lead. A step-down transformer 18 is connected inparallel with the line current through a pair of leads 20 and 22.

The high side of a main step-down transformer 24 is connected to theline 12 through a lead 26. The high side of this transformer 24 isprovided with a plurality of taps 28, each of which is connected to thepair of tap switches 30 and 32 through an appropriate number of leads.For purposes of illustration, tap switch 32 will be referred to as thehigh temperature tap switch, while tap switch 30 will be referred to asthe low temperature tap switch. The switch selector arm of each tapswitch is connected to a pair of contacts 34 and 36 through appropriateleads 38 and 40. Contacts 34 and 36 are associated with another pair ofcontacts 41 and 42 respectively, each of which may be connected to theline 12 through lamp indicators 44 (for contact 41) and 46 (for contact42).

The low side of the main step-down transformer 24 is connected to theends of an appropriate clamping 7. 2,828,405 Patented Mar. 25,-. 1.958

ice

mechanism, indicated. generally at 48,. through a pair of appropriatevleads 50' and5'2.v The clamping mechanism.48.canbeofanyconventionalshape or configuraa tion and its ends. are designed.to releasably' clamp a workpiece W. The clampingmechanism48 may have apair of pivoted clamping elements spring-biased to-. ward'each'otherwithelectrodes54. and 56 on its ends so. as to rigidly clamp. a.workpiece W between them.- With a workpiece positioned between the twoelectrodes, the circuit for the lowside-ofithemain step-downtransformer. will be completed.

A toroidal coil 58 may surround the" lead 50 and is connected to anappropriate meter. 60'through a pair of leads. 62 and 64. The. meter 60is appropriately graduated so that the amount of current is readilyreflected and observable.

The low side ofthe step-down transformer 18' is con! nected in serieswith arelay coil 66 and by appropriate leads 68 and 70 to a thermostat72- positioned on the workpiece W adjacent the. electrodes. 54 and 56.The core 74 on the relay. coil 66 carries a pair of. contacts 76 and 78which engagev contacts 34 and 41, or 36 and 421 Itshould be. understoodthat the core 74 of this relay canbe spring-biased into one. positionand moved into. the other position when the relay 66 is. energized.

If. desired, a timing mechanism and. switch 77 can be put in one of mainline lads- 12. or 14 so that the unit will automatically. be deenergiiedafter a selected period of time. 7

The a use, operation. and function. ofmy invention are as follows:

To connect two aluminum pieces together, the heating period used isdependent upon the material used to connect the two workpieces. In myspecific case, I use a thermo-setting plastic which involves a curingprocess. This plastic sets after a certain period of time and anyadditional heat applied to such a connection will only burn the plastic.My unit has a main circuit and a secondary circuit jointed together by astep-down transformer 24. A pair of branch circuits form a part of themain circuit and connect a plurality of taps on the high side of thetransformer to the source of electric power. The taps are connected totwo tap switches which complete the branch circuits. An auxiliarycircuit controlled by the thermostat 72 includes the relay 66 and therelay selects one of the branch circuits.

Sections of aluminum tubing or the like in the form of workpieces W tobe secured together are positioned between the electrodes 54 and 56. Thethermostat element 72 is positioned on the workpieces W directlyadjacent the electrodes so that it will reflect the temperature of thejoint. The operator then positions the manually settable tap switches 30and 32 at selected positions to establish the desired upper and lowertemperature limits of the temperature range and closes the manuallyoperable switch 16. The thermostat 72 is normally open and the relay 66is not energized. Contacts 76 and 78 are spring-biased into engagementwith the contacts 36 and 42 so that the current passing through thestep-down transformer 24 is controlled by the high temperature tapswitch 32. As soon as the temperature of the workpiece W reaches theselected high temperature value, the thermostat 72 closes and energizesrelay 66 drawing the contacts 76 and 78 into engagement with contacts 34and 41. This closes the low temperature tap switch circuit, and thestepdown transformer 24 is then on the low temperature heat for theelectrodes 54 and 56. The temperature of the workpiece W will thengradually cool until in a short period of time the thermostat 72 willopen again and deenergize the relay 66. This reverses the contacts andthe high temperature tap switch 32 is in use again.

The lamps 44 and 46 are in parallel with the two tap switch circuits sothat the operatorcan quickly tell whether the unit is on low or high heaThe coil 58 with its meter 60 reflects whether the unit in general isoperating satisfactorily. Its primary function is to reflect whether ornot proper contact has been made between the electrodes 54 and 56 andthe workpiece W.

It should be understood that the tap switches 30 and 32 are manuallysettable so that the upper and lower temperature limits are adjustable.Each of the tap switches are shown as individually adjustable but theycould be suitably connected together so that they would be adjustedtogether while being disposed at a fixed angle with respect to eachother.

While I have shown and described. the preferred form of my device, itshould be understood that many alterations, modifications and changescan be made without departing from the inventions fundamental theme. Forexample, I have described the device as being used primarily forwelding, soldering, or joining together aluminum tubing; however, itshould be understood that the device can be used to heat any type ofworkpieces when the operator desires to hold the workpiece in atemperature range between upper and lower temperature limits for apredetermined period of time. The current used in the line 10 could alsobe any voltage. I have stated that the thermostat 72 is normally open;however, this could be reversed with the contacts 76 and 78 beingspring-biased intoengagement with the contacts 34 and 41. I, therefore,wish that my invention be unrestricted except as by the appended claim.

I claim:

In a device for electrically heating aluminum tubing workpieces and thelike, a main circuit adapted to be connected to a source of electricpower, a secondary circuit with a pair of electrodes adapted to engagethe aluminum tubing workpieces to be heated, a step-down transformerbetween themain and secondary circuits with its low side in thesecondary circuit, the main circuit including a pair of parallel branchcircuits, each completing the main circuit between the high side of lthe transformer and the source of electric power, two

sets of control switches in the branch circuits, the high side of thestep-down transformer having a plurality of taps, each of the branchcircuits including a manually adjustable tap switch connected to thetaps, the tap switches being 'in parallel, each having contactsconnected to all of the taps, auxiliary circuit connected to andenergizable by the main circuit by an auxiliary step-down transformer,the auxiliary circuit including a temperature responsive switchresponsive to the temperature of the aluminum tubing workpieces foropening and closing the'auxiliary circuit, and a relay in the auxiliarycircuit controlling the sets of control switches for closing one set ofcontrol switches when the tem perature responsive switch is closed,thereby. closing the auxiliary circuit, to energize one branch circuitand for closing. the other set of control switches when the temperatureresponsive switch is open, thereby opening the auxiliary circuit, .toenergize the other branch circuit.

References Cited in the file of this patent

